A fixed guide and a movable guide, both of which are In sliding contact with a flexible transmission medium, may be used respectively to guide the transmission medium and maintain proper tension therein in order to prevent vibration and wobbling of the transmission medium, and to prevent transmission failure due to excess tension or excessive loosening of the medium.
The guide 500 shown in FIG. 4 is an example of a chain guide which exhibits excellent mechanical strength and wear resistance. In this guide, a core 510a of a slide rail 510 extending along the direction of travel of the transmission medium, and a core 520a of a support 520, which supports the slide rail 510, are formed as a unit from a glass fiber reinforced polyamide 66 resin. The entire structure consisting of both cores is covered by a skin composed of a polyamide 66 resin. The skin consists of a layer 510b, coating the outer surface of the core 510a of the slide rail 510, and a layer 520b, coating the outer surface of the core 520a of the rail support 520. Details of the guide structure and composition are described in the specification of Japanese patent publication No. 2004-125139 at page 2, and shown in FIGS. 3 to 6.
As shown in FIG. 4, the core 510a of the slide rail 510 and the core 520a of the rail support 520 are integrally fused to each other when the cores are molded, and are reinforced by coating the entire guide with a polyamide 66 resin. Thus, a strong connection is provided between the slide rail 510 and the rail support 520 so that the chain can be guided, and tension can be maintained over a long period of time.
In the conventional guide 500, the skin layer 510b formed in the slide rail 510, on which the chain slides is thin. When this skin layer 510b wears, the core 510b becomes exposed, and the glass fibers contained in the fiber-reinforced polyamide 66 resin exert an abrasive action similar to that of an abrasive material between the guide and the chain. Thus, the exposed glass fibers can promote wear of the guide.
In the operation of the conventional guide, both the skin layer 510b and the core 510a accumulate heat. However, because of the difference in the thermal properties of the glass fiber reinforced polyamide 66 resin forming the core 510a and the polyamide 66 resin forming the skin layer 510b, thermal deformation occurs between the skin layer 510b and the core 510a. If the difference in thermal properties is excessive, cracks are generated and the core 510a and the skin layer 510b may separate, causing reduction in the strength of the guide.
Accordingly, an object of the invention is to solve the above-mentioned problems encountered in prior art guides, and to provide a guide which suppresses heat accumulation in the rail on which the transmission medium slides, so that thermal deterioration is reduced, and smooth sliding contact with the traveling transmission medium, and satisfactory strength, are maintained over a long period of time.